Various forms of optical switches are known; however, at present, large 1.times.n cross-point optical switches are often configured to obtain functionality provided by n.times.m matrix switches. In some instances, reliability and cost are reasons for using this "dated" technology in an n.times.m configuration.
U.S. Pat. No. 4,580,873 in the name of Levinson issued Apr. 8, 1986 to AT&T Bell Laboratories describes a different type of n.times.m optical switch formed on a semiconductor; U.S. Pat. No. 4,988,157 in the name of Jackel et al. describes an n.times.m optical switch similar to that of the '873 patent, however wherein the presence and absence of air bubbles are used in place of movable mirrors to provide selectable reflective/transmissive cross points. Although in principle both of these devices appear to perform their intended function, neither of these switches has been commercialized on a large scale. Furthermore, the reliability of these devices in not yet known.
Thus, today, currently available switching matrices are being manufactured by use of a single stage architecture where both input and output sides of a P.times.P matrix are comprised of 1.times.P rotary switches. A rotary switch of this type is described by Duck et al. in U.S. Pat. No. 4,378,144. Duck et al. propose an arrangement wherein a faceplate comprising a number of collimating lenses along a pitch circle is attached directly to a stepping motor, the shaft of the motor being coaxial with the pitch circle. A rotatable arm with a collimating lens is attached to the shaft for rotation along the pitch circle, with a small distance therebetween, so that the lens of the arm can be optically connected with the lenses on the faceplate when the rotatable arm is moved by means of the shaft of the stepping motor. An optical input fibre is connected to the collimating lens (hereafter called a lens-to-fibre unit) of the arm and a plurality of optical output fibres are attached to the respective collimating lenses on the faceplate for a switching operation when the rotatable arm moves from one position to another.
Configuring a plurality of 1.times.P rotary switches into a single stage P.times.P switch has the following limitations:
a) the P.times.P matrix is not modular and when repairs are required, they must be made to the entire switch; PA1 b) the cost of the switch is largely dependent upon the cost of the number lens-to-fibre units required; and, PA1 c) The maximum reconfiguration time of the component 1.times.P rotary switch is directly dependent upon the dimension of the matrix. PA1 M first ports, where M&gt;1; PA1 MR second ports where R&gt;1, for optically coupling to second ports of other modules; PA1 and switching means for switching between the M first ports and the MR second ports wherein at least a second port of a module is directly coupled to another second port of another module. PA1 M first ports, wherein M is at least P/R; PA1 MR second ports; PA1 and switching means for switching between the first ports and the MR second ports, wherein the MR second ports of a module are optically coupled to second ports of other modules. PA1 providing a first group of functionally identical modules each module including M first ports and MR second ports and switching means for switching between the first ports and the second ports; PA1 providing a second group of functionally identical modules, each module including M first ports and MR second ports and switching means for switching between the M first ports and the MR second ports; PA1 interconnecting the second ports of the first group of modules with the second ports of the second group of modules wherein some second ports from each module in the first group of modules are connected to some second ports of each module in the second group of modules. PA1 a plurality of M first ports; PA1 MR second ports optically coupled to second ports of other modules; PA1 and switching means for switching between the first ports and the second ports.
It is usually preferable that optical switches be efficient, fast and compact. As telecommunication networks have evolved over the years and have become more complex, a need has arisen for a matrix switching system capable of optically coupling any one of a large number of other fibers to another. Furthermore, it is desirable for the switching system to be "non-blocking", i.e. the switching of one input fiber to an output fiber should not interfere with the light transmission of any other input fiber to any other output fiber.
It is an object of this invention, to provide a modularized non-blocking switch that can be configured from 1.times.n switches, or switches of other dimensions, that require fewer lens-to-fibre units than the P.times.P single stage switch.
It is a further object of the invention, to provide a modularized non-blocking switch that is less expensive to manufacture than the P.times.P single stage switch.